1. The importance of controlling the fineness of raw meal. For a long time, the fineness of raw meal has not received too much attention in the cement production process. This is because: this indicator is relatively easy to achieve, and it is very important for the next step. There is no impact on the production of the process. There are also many people who believe that the finer the raw material fineness, it can only bring benefits to the clinker production of the kiln by increasing production and reducing consumption. Therefore, they do not pay too much attention to this indicator. In fact, from the perspective of fine operation, the reasonable formulation of this indicator is of considerable positive significance. (1) The finer the raw meal, the better. This is not only directly related to the power consumption and output of the raw meal mill, but also to the output and heat consumption of the kiln. With the further popularization of new dry processes, more and more people have realized that too fine raw materials will have the following disadvantages: fine powder does not have much advantage over coarse powder in heat transfer in the preheater. On the contrary, it The residence time in the pipe is short, and it is the part in the preheater that is least likely to be separated from the hot air flow. It is easier to escape from a certain level of preheater to the upper level preheater, and at the same time, the received heat transfer is to the upper level. , increasing heat consumption; fine powder easily enters the exhaust gas treatment system, which increases the amount of dust contained in the exhaust gas, which wastes both heat and electricity; during the storage process of raw materials, fine powder easily agglomerates, which is not conducive to removal from the warehouse and homogenization, resulting in more uneven particles, which is not conducive to powder selection and heat transfer in the preheater as well as heat transfer and calcination in the kiln. (2) The requirements for the particle size range of raw meal are completely different from the particle size distribution range of cement. The narrower the particle distribution of raw meal, the better. Because fine raw material powder not only wastes energy during the preparation process, but also has the above-mentioned adverse effects on the next calcination process; while coarse raw material powder will increase the difficulty of calcination, resulting in higher fCaO remaining in the clinker, and excessive amounts of fCaO. Fuel consumption. The practice of many factories at home and abroad has proven that raw materials less than 200?0?8m can meet the needs of clinker calcination, and its sieve allowance is far more important than that of less than 90?0?8m. The advanced power consumption level of the raw material host should be: for ball mills, when grinding soft materials, the main motor is about 10 kWh/t, and for hard materials it is 25 kWh/t; for vertical mills, this range is 4.5 to 8.5 kWh /t, although the power consumption of the fan will increase, the system power consumption is still 30% lower than that of the ball mill. At present, there are not many companies that can reach this level. It should be said that starting from the formulation of fine-grained indicators, we can find ways to narrow this gap. 2. Control standards for raw meal fineness. The optimal fineness of raw meal should be determined by raw material experiments and production practices of each factory. The determination principles are: (1) As long as it is within the allowable range of the kiln’s calcination, the raw meal particle size should be Be bold. Generally speaking, the raw meal should be ground until the sieve allowance of 170# (90?0?8m) is 15, and the sieve allowance of 50# (300?0?8m) is 1.5~2.5. Most companies have basically mastered this control principle. In fact, according to the above theoretical basis, the fineness can still be further increased. Therefore, some production lines have adjusted the raw meal fineness to 80?0?8m sieve allowance 22, and the effect is very good. Under the conditions that meet and are favorable for calcination, the output of the mill is increased and the power consumption is reduced, killing three birds with one stone. (2) Increase the control index of 200?0?8m screen clearance. Most domestic production lines still use the control of 80?0?8m as the assessment indicator, and do not inspect the 200?0?8m screening margin. The result of this control may be: even if the screen clearance control of 80?0?8m is relaxed to 15, it does not mean that the screen clearance greater than 200?0?8m must be very small. Once the calcining of the kiln is affected, it is difficult to draw a conclusion whether it is because the 200?0?8m sieve allowance is too small or the 80?0?8m sieve allowance is too large. On the contrary, if the screen allowance of 200?0?8m can be controlled below 2, the calcining condition of the kiln is very good. Can the screen allowance of 80?0?8m be made too large in order to save energy and increase production? This is the need for precision operation. Do the work. 3. Control method of raw meal fineness (1) It is very easy to adjust the speed of the powder separator of vertical mill and closed-circuit ball mill through frequency conversion, thereby achieving control of raw meal fineness.
But narrowing the fineness range of its products will be much more difficult. (2) Promote the use of LV technology. A few years ago, LV Company used its patented technology to transform the LSK powder separator in the vertical mill. The transformation not only increased the rising speed of the air flow, but also reduced the pressure drop and reduced wear on the rotor. The principle is to design a stator with several LV air chambers in a circle, so that the coarse particles carried by the rising airflow are clearly separated from the fine particles of the finished product, and the coarse particles are no longer separated from the rising ones when they fall back to the grinding disc. The particles collide, thus avoiding energy loss. And because the material returned by collision is reduced, the thickness of the material on the grinding plate also tends to be stable. Not only can the feeding amount be increased, but the overflow of the material can also be reduced by at least half. And because the airflow speed through the LV air chamber can be adjusted according to the particle size of the raw material, through its powder selection, not only there is no coarse material in the selected fine powder, but also there is no fine powder in the falling coarse material, reaching the product The purpose of narrowing the particle size range is in line with the requirements for the fineness composition of the raw meal. This technology has been widely promoted abroad, and a few factories in China, such as Yunfu, have been transformed, and the results are very satisfactory. This technology patent has been successively purchased by companies such as Feifei and Smith in recent years. Therefore, there is no need to modify the newly purchased vertical mills. In addition, for systems that use ball mills to produce raw materials, there are also corresponding LV technologies to transform their powder concentrators. 4. Inspection methods for raw meal fineness. The production of mills requires both continuous online analysis system supervision and experimental analysis of hourly instantaneous samples or mixed samples. Fineness inspection samples can come from testing raw meal ingredients. For samples, the inspection frequency can be once every 4 hours when production is stable. During sampling, attention should be paid to the cleanliness of the raw material, otherwise it will seriously damage the control program of the analyzer and also affect the fineness test results. Many foreign laboratories are equipped with online laser particle size analyzers, which can provide particle size distribution data of raw materials. The focus range is 0.1~200?0?8m: for vertical mills, the circulation time of materials is usually less than 1 min, while for ball mills It will take more than ten minutes. Therefore, the response time of the control must be as fast as possible to facilitate the control of the automatic control loop.